Total reflection x-ray analysis (TXRF), x-ray reflectometry (XRR), grazing incidence x-ray diffraction (GIXRD), grazing incidence diffraction (GID), and grazing incidence small angle x-ray scattering (GISAXS), are well-established x-ray surface analysis and measurement techniques [see, for example, R. Klockenkiimper and A. von Bohlen, Total Reflection X-ray Fluorescence Analysis and Related Methods 2nd Ed. (J. Wiley and Sons, 2015); R. Fernandez-Ruiz, “TXRF Spectrometry as a Powerful Tool for the Study of Metallic Traces in Biological Systems” Development in Analytical Chemistry Vol. 1 2014; M. Birkholz, “Chapter 4: Grazing Incidence Configurations”, in Thin Film Analysis by X-ray Scattering (Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 2005); and G. Renaud et al., “Probing surface and interface morphology with Grazing Incidence Small Angle X-ray Scattering” Surface Science Reports vol. 64:8 (2009), pp. 255-380]. These grazing incidence techniques utilize an X-ray beam incident upon a sample surface with an incidence angle smaller than the critical angle for total reflection of the surface material at the incident x-ray energy. Under this condition, the incident x-rays penetrate only a short distance into the surface, typically less than 20 nm, resulting the surface sensitivity of the techniques.
TXRF provides highly sensitive chemical composition and concentration analysis and quantification of a thin surface layer (<20 nm) of a sample with a flat surface or a sample (e.g. liquid or fine particles) on top of an optically flat substrate by measuring the x-rays produced by the sample under x-ray excitation. It may also be used to determine the thickness of a thin film on top of an optically flat substrate.
XRR measures the intensity of x-rays undergoing specular reflection from a surface at various angles of incidence to obtain density, thickness, and roughness profiles of surface layers and thin films.
GIXRD is useful for crystalline structural determination of a thin surface layer of a sample with a flat surface by measuring diffraction patterns resulting from an x-ray beam at a grazing incidence angle. This is typically used with flat surfaces. GID records the diffraction pattern at a grazing exit angle.
GISAXS is useful to characterize structures (typically with dimensions on a namometer scale) of a thin surface layer of a sample as well as inner electron density fluctuations of the deposited material by measuring the scattering signal that results from an x-ray beam of grazing incidence.
For scientific studies of materials that need high brightness x-rays, high brightness synchrotrons or free-electron lasers have been used with great success. However, these facilities are large, often occupying acres of land, and expensive to operate, and obtaining beamtime can take months of waiting. They are impractical for conventional laboratory use.
Until now, laboratory application of the grazing incidence x-ray techniques described above have relied on conventional laboratory x-ray sources that use an extended solid metal anode (such as copper) and have relatively low brightness and limited choice of x-ray spectra of the incident x-ray beam, due to limitation of the x-ray target anode materials with suitable thermal, mechanical, and chemical properties that are required to ensure continuous operation of the x-ray target, typically preventing the anode target from melting, as disclosed in U.S. Pat. Nos. 5,249,216 and 6,829,327, whose disclosures are incorporated herein by reference in their entirety, have disclosed TXRF system designs using existing laboratory x-ray sources.
U.S. Pat. No. 7,929,667, also incorporated herein by reference in its entirety, describes the use of an x-ray source using a liquid metal jet anode to circumvent the thermal limitations of conventional x-ray sources for x-ray metrology applications. However, to achieve the desired benefit, the metal jet needs to be in liquid form and have sufficiently high speed and low vapor pressure, among other challenging requirements. The major limitation of this type of x-ray source is that only an extremely limited number of metals are in liquid form at reasonable temperatures, i.e., below 200 centigrade. Consequently, the choice of x-ray characteristic lines for monochromatic x-ray beam illumination is extremely limited.
To make substantial performance improvements to grazing incidence x-ray techniques, singularly or in combination, there is need of an x-ray apparatus comprising a high brightness laboratory x-ray source, preferably providing flexibility in choice of anode material to produce a range of x-ray energies. Additionally, among these techniques, there is also continued demand for reducing (improving) absolute and/or relative trace element detection limit in liquids and solutions, especially for low atomic number elements (e.g. boron (B), carbon (C), oxygen (O), fluorine (F), sodium (Na), aluminum (Al), and sulfur (S)), improving throughput, quantitative elemental composition analysis accuracy, higher spatial resolution for small spot analysis or mapping/imaging of elemental composition as well as higher sensitivity and performance in determining crystallographic phases and/or texture, measurement of thin film thickness, semiconductor metrology, and measurement of impurities and contamination on silicon surfaces in semiconductor manufacturing.